1. Field of the Invention
The present invention relates to a disk drive in which a head reads and writes data from and to a disk, and more particularly to a disk drive and emergency head-unload control circuit suitable for quickly retracting (unloading) a head to a retract area when the drive is dropped.
2. Description of the Related Art
Hard disk drives (HDDs) are well known as typical disk drives in which a head reads and writes data from and to a disk. HDDs have recently been made compact. For instance, HDDs used as storage for notebook-type personal computers (portable computers) are mainly 2.5-inch HDDs. Further, 1.8-inch, 1-inch and even 0.85-inch HDDs have appeared. In accordance with reduction of HDD size, various portable electronic devices (hosts) have also appeared. In those small-size electronic devices, there is an increasing danger that users may unintentionally drop them. If a user drops their electronic device in use, the head may well collide with the disk thereby damaging the head and/or disk.
In light of the above, Japanese Patent No. 2536985 discloses a technique for retracting the head to a retract area by executing a predetermined routine using a dedicated processor or central processing unit (CPU), when an electronic device with an HDD, such as a portable computer, is dropped. This technique can prevent the head from colliding with the disk when the electronic device is dropped, thereby protecting the head and disk from damage.
To prevent the head and disk from being damaged because of dropping, it is necessary for the electronic device to execute a predetermined program to unload the head within a period shorter than the period required for the electronic device to drop. However, not all electronic devices with HDDs installed can execute such a program at high speed.
Furthermore, the head and/or disk of an HDD may be damaged for a reason other than the drop of an electronic device with the HDD. For instance, also when the supply of power to an HDD (or an electronic device with the HDD) is interrupted during the operation of the HDD, the head and/or disk may be damaged. Jpn. Pat. Appln. KOKAI Publication No. 2000-21073 discloses a technique for using a capacitor, charged with electricity, for quickly retracting the head to a retract area when power from the power supply is interrupted. This technique, however, does not consider the problem that occurs during dropping an electronic device with an HDD.